Electronic devices use power to operate. Switching power converters are commonly used due to their high efficiency, small size and low weight to power many of today's electronics. Conventional wall sockets provide a high voltage alternating current. In a switching power converter a high voltage alternating current (ac) input is converted to provide a well regulated direct current (dc) output through an energy transfer element. The switching power converter typically includes a controller that provides output regulation by sensing the output and controlling it in a closed loop. In operation, a power switch is utilized to provide the desired output by varying the duty cycle (typically the ratio of the time the power switch is able to conduct current over a certain time period) of the switch to control the transfer of energy between the input and the output of the power converter. The controller of the power converter may provide output regulation by adjusting the duty cycle of the power switch in response to sensing the output. In operation, the switch may produce a pulsating current having a frequency regulated by the controller to produce a substantially constant output current at the load.
In one example, a controller of a switching power converter may be designed to perform a power factor correction and regulation. More specifically, power factor correction allows for the input current to proportionately change with the ac input voltage to increase power efficiency. In many power converter circuits, the power factor correction feature that is included may require the controller to operate in different control modes to achieve optimal efficiency while regulating within a certain tolerance. A drawback of this approach, however, is that the inclusion of multiple control modes must be implemented with additional inputs which may increase the need for additional pins on the controller of the power converter, thus increasing the cost of the controller.